1. Field of the Invention
The present invention relates generally to microbial fuel cells (MFCs) and, more particularly to an energy conversion system that efficiently collects, stores, and converts the trickling energy continuously produced by a microbial fuel cell into a form that is compatible with conventional storage devices and/or electronic systems.
2. Description of the Prior Art
Microbes have inhabited the seafloors around the world since the early days of this planet's existence. Such seafloor regions are anaerobic wherein the microbes gain energy by using the prevalent iron oxides and organic matters found on the seafloor. By colonizing conducting surfaces that act as sinks of electrons, microbial fuel cells (MFCs) convert organic matter to electricity.
A MFC system is typically a large array of conductive plates deployed on the ocean floor. Approximately half of these plates are positioned in the ocean floor sediment (anodes) and the rest of the plates are suspended in water above the ocean floor (cathodes). Microbes colonize these plates and convert organic matter prevalent on the seafloor to electricity, which is collected by the conductive plates. The anodes become negatively charged and the suspended cathodes become positively charged.
The open-circuit or unloaded voltage potential present between the anodes and cathodes has been found to range from approximately 0.6VDC to 0.8VDC. However, the loaded MFC voltage output may decrease significantly as an external electrical load is applied between the anodes and corresponding cathodes.
Individual cables may be attached to the anodes and cathodes of the MFC system, brought to the surface and/or to an underwater position, and may be connected in parallel at the input to the power converter/storage system described in this disclosure.
Unattended sensors used in an ocean environment typically require the replacement of batteries in which this replacement involves considerable logistics and time. In difficult to reach locations, the replacement cost might even be on the order of $100K/sensor.
Most commercially available oceanographic equipment, including sensors, lanterns, and acoustic pingers are battery-operated and require supply voltages from 3VDC to 24VDC to operate. Traditionally, such sensors require on-board batteries for power. Such devices cannot be directly powered from the MFC. In addition, such devices may often have continuous power ratings in excess of what is continuously available from the MFC.
Furthermore, commercially-available power converters are unsuitable for use with MFCs. All known commercially-available voltage converters have a minimum voltage input requirement that is at least 4-5 times greater (2-3VDC) than the maximum voltage available from the MFC. In addition, these converters require input current levels in excess of those available from the MFC. Previously-developed MFC power conditioners have been found to be unsatisfactory due to the difficulties of harvesting the highly variable and low voltage/current outputs of such fuel cells.
The following U.S. patents describe various prior art systems that may be related to the above and/or other MFC power conditioners:
U.S. Pat. No. 5,976,719 teaches a biofuel cell which can react with an electrode without mediator. The microorganism of a biofuel cell can directly consume the electrons generated from a fermentative metabolism of the microorganism through an electron metabolism without energy conservation. Therefore, if waste water is utilized as a fuel (substrate) in the biofuel cell, the amount of sludge production will be reduced and the efficiency of catabolizing organic materials will be increased.
U.S. Pat. No. 5,427,871 relates to galvanic seawater cells and batteries and in particular to cathodes which are suitable for use in galvanic cells that use an oxidant dissolved in the electrolyte as depolarizer. An example of such cells is a seawater cell which uses the oxygen dissolved in the seawater as oxidant. The cell has an inert electrode which consists of a number of conducting fibers connected to a conducting body. The fibers have different orientations relative to each other and to the body. The electrode body consists of two or more wires which are twisted together to constitute an electrode stem while clamping the fibers in a fixed position between the wires, as in a laboratory bottle brush.
U.S. Pat. No. 6,913,854 teaches generating power from voltage gradients at sediment-water interfaces or within stratified euxinic water-columns. Natural voltage gradients typically exist at and about sediment-water interfaces or in isolated water bodies. One electrode (anode) is positioned in the sediment or water just below the redox boundary and the other electrode (cathode) is positioned in the water above the redox boundary over the first electrode. The anode is lower in voltage than the cathode. Current will flow when the electrodes are connected through a load, and near-perpetual generating of worthwhile power may be sustained by the net oxidation of organic matter catalyzed by microorganisms.
U.S. Pat. No. 7,160,637 teaches a miniaturized microbial fuel cell which derives electrical power from the biological activity of microbes, typically the metabolism of glucose by baker's yeast. Microfabrication techniques are used to miniaturize the components as well as the overall fuel cell and are capable of integration with other biomedical and implantable devices. Substantial reductions in both the size and the cost of implantable systems are thereby achievable. Electrode structures are used that facilitate electron transfer and power production giving favorable power densities in a miniature fuel cell. In addition, the microbial fuel cell of the present invention extracts glucose or other metabolite(s) from the ambient body fluids as its fuel, thus achieving a renewable, long-term power source for implantable biomedical devices.
U.S. Pat. No. 7,491,453 teaches systems and processes for producing hydrogen using bacteria. One process for producing hydrogen uses a system for producing hydrogen which includes a reactor. Anodophilic bacteria are disposed within the interior of the reactor and an organic material oxidizable by an oxidizing activity of the anodophilic bacteria is introduced and incubated under oxidizing reactions conditions such that electrons are produced and transferred to the anode. A power source is activated to increase a potential between the anode and the cathode, such that electrons and protons combine to produce hydrogen gas. The system includes a reaction chamber having a wall defining an interior of the reactor and an exterior of the reaction chamber. An anode is provided which is at least partially-contained within the interior of the reaction chamber and a cathode is also provided which is at least partially contained within the interior of the reaction chamber. The cathode is spaced apart at a distance in the range between 0.1-100 centimeters, inclusive, from the anode. A conductive conduit for electrons is provided which is in electrical communication with the anode and the cathode and a power source for enhancing an electrical potential between the anode and cathode is included, which is in electrical communication with the cathode. A first channel defining a passage from the exterior of the reaction chamber to the interior of the reaction chamber is also included.
U.S. Pat. No. 7,507,341 teaches a method of converting biological material into energy resources, which includes transmitting biological material to a pulsed electric field (PEF) station, and applying a PEF to the biological material within a treatment zone in the PEF station to generate treated biological material. The method also includes transmitting the treated biological material to a biogenerator, and processing the treated biological material in the biogenerator to produce an energy resource. A converter may carry out this process, and may include the PEF station and the biogenerator.
United States Publication No. 2007/0048577 teaches a fuel cell having: a proton exchange membrane; anode and cathode housings containing chambers; a three-dimensional anode and cathode. Each housing may have a feed passage, a waste passage, and two through passages. The anode feed passage and the anode waste passage are each coupled to the anode chamber and to one of the cathode through passages and vice versa. The anode chamber may have bacteria capable of donating electrons to the anode upon exposure to a fuel. Solutions may be circulated through the passages and chambers.
United States Publication No. 2007/0134520 teaches power generation performed by immobilizing an electron mediator having a standard electrode potential at pH 7 in the range of −0.13 V to −0.28 V to one of a pair of electrodes to form an anode and electrically connecting the other electrode as a cathode to the anode to form a closed circuit, bringing the anode into contact with microorganisms capable of growing under anaerobic conditions and a solution or suspension containing an organic substance to advance the oxidation reaction by microorganisms using the organic substance as an electron donor, separating the cathode and the solution or suspension through an electrolyte membrane to advance the reduction reaction using oxygen as an electron acceptor at the cathode, and accelerating the oxidation reaction in the biological system.
U.S. Publication No. 2007/0259216 teaches a microbial fuel cell configuration which includes a substrate particularly formulated for a microbial fuel cell configured to produce electricity and/or a modified microbial fuel cell configured to produce hydrogen. A substrate formulation includes a solid biodegradable organic material in a package porous to bacteria. A microbial fuel cell includes an anode, a cathode, an electrically conductive connector connecting the anode and the cathode, a housing for an aqueous medium, the aqueous medium in contact with the anode, and a solid form of a biodegradable organic substrate disposed in the aqueous medium. The solid form of a biodegradable organic substrate is formulated to support electron generation and transfer to the anode by anodophilic bacteria over a selected minimum period of time.
The above-cited prior art does not disclose a circuit that can realistically be utilized to harvest power from an MFC—over an extended period of time. As such, a continuing need exists for the solutions to power problems such as the above described problems and/or related problems. Consequently, those skilled in the art will appreciate the present invention that addresses the above and other problems.